1. Field of Invention
The present invention relates to an internal and external electrotherapy apparatus to apply an electric stimulation pulse onto the patient and its electric energy delivering method, and specifically to an electrotherapy apparatus effective in terminating the fibrillation of hearts in cardiac diseases, and its electric energy delivering method.
2. Related Art
In patients having cardiac diseases, the fibrillation is an important factor which causes the patient' death. In order to terminate the fibrillation, an electrotherapy apparatus (called defibrillator) which applies a shock by an electric stimulation pulse (called defibrillation pulse) onto the heart of the patient and terminates the fibrillation, is commonly used.
The internal defibrillator is adjusted and used for only an individual patient, therefore, because the impedance between electrodes is a value inherent to the patient and almost constant, the waveform can be adjusted so that the defibrillation efficiency becomes optimum for the impedance of the patient. On the other hand, in the external defibrillator, the higher current output than that of the internal type is necessary, and further, because the impedance is used for various unspecified patients, when the fibrillation is not terminated by the first electric shock, a method of delivering shock again with the increased energy value is applied.
Further, as the waveform, there are a monophasic type and a biphasic type, and recently, the biphasic type in the both is known to have advantages that the output electric energy may be smaller than that of the monophasic type, the energy efficiency is high, and the damage to the patient is small.
Referring to the drawing, an output circuit of the conventional biphasic defibrillator will be described below. FIG. 10 is a view for explaining the output circuit of the conventional biphasic defibrillator, and FIG. 11 is a view of its waveform.
FIG. 10(a) is an example in which a mechanism to reverse the phase by four switches is provided, and the mechanism has a capacitor 201 to store the electric energy, switches 202, 203, 204, and 205, and output electrodes 206a, and 206b. This is the technology disclosed in U.S. Pat. No. 4,850,357 (JP-B-4-45193).
In this biphasic defibrillator, when the first phase (positive phase) waveform electric pulse is outputted, the switches 202 and 205 are turned on, and switches 203 and 204 are turned off, and thereby, the positive polarity voltage of the capacitor 201 is applied on the output electrode 206a, and the negative polarity voltage of the capacitor 201 is applied on the output electrode 206b, and from these electrodes, the positive phase truncated exponential waveform electric pulse is applied to the patient 207 (impedance of the patient: 207a). Then, when the voltage or time comes to a predetermined value, the switches 202 and 205 are turned off.
Next, in the case where the second phase (negative phase) waveform electric pulse is outputted, when the switches 203 and 204 are turned on, the negative polarity voltage of the capacitor 201 is applied onto the output electrode 206a, and the positive polarity voltage of the capacitor 201 is applied onto the output electrode 206b, and from these electrodes, the negative phase truncated exponential waveform electric pulse is applied onto the patient 207. Then, when the voltage or time comes to a predetermined value, the switches 203 and 204 are turned off.
According to that, from the output circuit of the above conventional biphasic defibrillator, the truncated exponential biphasic waveform as shown in FIG. 11(a) can be obtained.
Further, FIG. 10(b) is an example in which a mechanism to reverse the phase by 2 capacitors is provided, and the mechanism has capacitors 211 and 212 to store the electric energy, switches 213 and 214, and output electrodes 215a and 215b. This is a technology disclosed in the U.S. Pat. No. 5,871,505.
In the biphasic defibrillator, in the case where the first phase (positive phase) waveform electric pulse is outputted, when the switch 213 is turned on, and the switch 214 is turned off, the positive polarity voltage of the capacitor 211 is applied onto the output electrode 215a, and the negative polarity voltage of the capacitor 211 is applied onto the output electrode 215b, and from these electrodes, the first phase (positive phase) truncated exponential waveform electric pulse is applied onto the patient 216 (the impedance of the patient: 216a).
Then, when the voltage or time comes to a predetermined value, the switch 213 is turned off.
Next, when the second phase (negative phase) waveform electric pulse is outputted, the switch 214 is turned on, and the switch 213 is turned off, thereby, the negative polarity voltage of the capacitor 212 is applied onto the output electrode 215a, and the positive polarity voltage of the capacitor 212 is applied onto the output electrode 215b, and from these electrodes, the second phase (negative phase) waveform electric pulse is applied onto the patient 216.
It According to that, the biphasic waveform as shown in FIG. 11(b) is obtained from the output circuit of the above conventional biphasic defibrillator.
A publicly known example disclosed in the U.S. Pat. No. 5,591,209 is for the implantable defibrillator, and a method in which the first phase applies the energy stored inhigh voltage storage capacitors onto the heart, and the second phase directly applies the energy from the battery source in low voltage onto the heart, is shown.
In the technology of the implantable defibrillator having the low output energy disclosed in the U.S. Pat. No. 5,350,403 (JP-A-6-47100), a control unit is provided between a charging capacitor and the electrode, and by turning on or off the circuit, the electric pulse having a predetermined current curve is applied onto the patient.
The U.S. Pat. No. 5,607,454 (JP-A-9-500309) uses the truncated exponential curve. With this method, the durations of the waveforms of the first phase and the second phase are changed depending on the impedance of the patient.
Comparing to the monophasic defibrillator, the conventional biphasic type defibrillator, for example, in the case of FIG. 10(a), 4 switches are necessary, and further, in the case of FIG. 10(b), 2 electric energy storage section (capacitor) are necessary, and the number of elements is increased as compared to the monophasic defibrillator.
Generally, in the defibrillator, in order to generate the high voltage from the low voltage power source such as a battery, even when the number of the electric energy storage sections (capacitor) and switches (structured by superimposing a plurality of stages of semiconductor switches) is increased by, for example, only one, the apparatus becomes larger and heavier, therefore, problems that the portability in the emergency circumstances is lowered, or the like, are caused, and further, the cost of the overall apparatus is also increased.
In the output system of the conventional truncated exponential waveform as disclosed in the U.S. Pat. No. 5,607,454 (JP-W-9-500309), the impedance of the patient directly influences the decay of the voltage of the capacitor, and the time constant is unconditionally determined, and as the control to form the waveform, it can operate only when the waveform output is completed (truncated).
Further, in the external defibrillator, because the electric stimulation pulse is applied transthoracically, the impedance applied across output electrodes during operation is different depending on the patient (inherency), and further, the large difference is generated depending on the physical and physiological difference of the patient.
Further, in the following references 1 and 2, when the time period in which the electric pulse is applied, is not within a predetermined time period, the effective defibrillation can not be carried out.
Reference 1: Koning G. Schneider H. Hoelin A J. et al. “Amplitude-duration relation for direct ventricular defibrillation with rectangular pulses.” Medical & Biological Engineering, 1975 May: on page 388-395.
Reference 2: “Ventricular Defibrillation Using Biphasic Waveforms: The Importance of Phasic Duration” JACC 1989 January 13:1 207-14.
Accordingly, when the sufficient electric energy can not be delivered within this effective period, even when the electric pulse is continuously applied over this period, there is a problem that the effect of the defibrillation can not be increased.
Accordingly, when the impedance of the patient is high, because only by the output of the conventional truncated exponential waveform, it takes a lot of time to deliver the electric energy to the patient, the sufficient energy can not be delivered within the effective period to apply the defibrillation pulse, and therefore it unavoidably truncates the output of the defibrillation pulse.
Further, in the technology disclosed in the U.S. Pat. No. 5,591,209, the energy stored in the high voltage storage capacitors is used only for the first phase waveform. Accordingly, all the energy stored in the capacitors is not used for the defibrillation.
That is, in such the waveform, because the first phase is completed under the condition that the voltage of the capacitors is lowered to about 40%, it comes to an account that about 16% of overall amount of the energy stored in the capacitors are not used for the defibrillation.
In the external defibrillator, normally, it is necessary that the safety is secured by electrically isolating the circuit passing through the low voltage power source and the patient, (for example, some measures to isolate the patient at the time of the second phase output is provided), however, it is not disclosed in the above publicly known examples.
Further, when the technology in the above publicly known examples is applied for the external defibrillator, it is additionally necessary to provide the insulation circuit composed of transformer, or the like, to output the second phase other than the insulation transformer to store the energy in the energy storage section, and it is not preferable from the viewpoint of the size reduction to apply it for the external type.
Further, because the power source of the second phase is directly applied from the power source apparatus (battery source), the instantaneous maximum electric power applied on the patient is limited by the maximum electric power of the power source apparatus.
When such the system is applied for the external defibrillator, because the very large instantaneous electric power is required as compared to that of the internal defibrillator, when the capacity of the power source is not designed to be large, the effective defibrillation pulse can not be outputted. Generally, the inherency of the impedance value of the patient spreads to the range from 25 Ω to 125 Ω.
For example, in the second phase, in order to apply the voltage of 300 V to the patient, the power source capacity P shown by the following equation 1 is required.P=300 (V)2/25(Ω)=3600 (Watt)  (1)
As described above, because the very large power source capacity of 3600 (Watt) is necessary, it is difficult also from the viewpoint of the power source capacity to apply for the external defibrillation.
Further, because the power is not controlled in the second phase, the necessary energy can not always be delivered within the effective time period.
Further, in the technology disclosed in the U.S. Pat. No. 5,350,403 (JP-A-6-47100), the control unit which can turn on or turn off the circuit, is provided between the charging capacitor and electrode, and the maximum voltage value of the output waveform obtained at the time of the control can not be larger than the capacitor voltage obtained when the circuit is continuously turned on by the control unit.
This is the reason why the unit is structured such that the control unit is operated only in the direction to control the output.
Further, at the time of the defibrillation, when the impedance of the patient is large, there is a case in which it is preferable that the higher voltage than the voltage stored in the charging capacitor is supplied to the patient. In the conventional technology, in order to defibrillate in biphasic waveform, it is necessary that the 2 charging capacitors are additionally prepared, and the reverse of the polarity of the output voltage is conducted by using 4 switches (called H-bridge).